Added: Render for Option<T>

[re-oh]

impl<T: Render + ?Sized> Render for Option<T> {
    fn render_to(&self, w: &mut String) { if let Some(inner) = self { T::render_to(inner, w); } }
}

impl <T: Render + ?Sized, I: ExactSizeIterator + ?Sized> Render for I where I::Item: AsRef<T> {
    fn render_to(&self, w: &mut String) {
        for item in self {
            item.as_ref().render_to(w);
        }
    }
}

Implemented Render for 2 types:

• ExactSizeIterator since if it was infinite like: 0.. it would run forever. ( Not 100% sure if this implementation works, if anyone could tell me how i can test this it would be much appreciated since you dont need a owned value to render it. ergo AsRef<T> for I::Item)
• Option<T> Simple, if self is some render the inner value if not, dont render it. ( I think thats how @martinhath wanted it to work. )

If there are any suggestions for other types to implement or if my implementation has issues ill gladly fix them.

[re-oh]

Also removed the ?Sized bound on T for Option<T> since Apparently Option<T> needs for T to be sized.

[re-oh]

closes issue / feature request: #446